Topic: Phaedrus: CB750 RestoMod - Update: 09/23/21 w/ new video

[MCRider]

What carbs are we talking about?

Mikuni VM29 Smoothbores

[MRieck]

What carbs are we talking about?

I thought he was running Mikuni 29's. I forget which cam is in there. The rich condition...like you said....corresponds with the power graph. Main jet looks OK...drop the needle a couple of notches and see what happens.
 I believe a different exhaust system would really help. I think the Hindle 4/2/1 Ripple Rock Racers sells is a really, really nice system. Price is in Canadian dollars which sweetens the deal even more.

[MRieck]

 Ron....really no need to spin the engine that high.....party is over @ 9,500 with these engines. Your chart shows power flattening at 7,500 and the A/F is beginning to lean out towards 13-1. You are running out of cam and/or exhaust. I am sure the cam is timed correctly. What cam is in there???

[MCRider]

What carbs are we talking about?

I thought he was running Mikuni 29's. I forget which cam is in there. The rich condition...like you said....corresponds with the power graph. Main jet looks OK...drop the needle a couple of notches and see what happens.
 I believe a different exhaust system would really help. I think the Hindle 4/2/1 Ripple Rock Racers sells is a really, really nice system. Price is in Canadian dollars which sweetens the deal even more.

Its a CycleX 7. Ken says its a Mega Cycle 125/75 with 3 degrees more overlap.

Yeah, I'm struggling with the pipe. I first used a Marshall DeepTone 4-1. I chose it for aesthetics: wiggly header pipes, long megaphone, and since I wanted to tour on it, as I had with the first iteration of Phaedrus, it didn't have much kick up on the meg which would interfere with the over the seat saddlebags. Many negatives as it turns out. It was really poorly made, took us days to grind the chrome off the headers so they would slip into the collector. It also interfered with inspecting the oil pump, and hanging the oil cooler. It did sound good.

So I though I would go with something cheap and free flowing. Hence the Cycle X 4-2. Ken told me not to expect performance from the pipe.its just a pipe. But its made well, And gives full access to the oil pan and pump without removing it. I gutted a little bit of it to allow the DYNO sniffer into it. Its loud, but since I won't be riding it, just drags and maybe the LSR.

A Hindle is not out of the question.

[Jerry Rxman Griffin aka MuthaF'er]

Ron, borrow Joe's new RS34's for a run  I like the Mikuni 29's - for a stock/near stock bike. You're choking it down maybe? Let it breathe more.

[MRieck]

Ron, borrow Joe's new RS34's for a run  I like the Mikuni 29's - for a stock/near stock bike. You're choking it down maybe? Let it breathe more.

I don't think the carbs are the problem Jerry. the main obstruction to flow is the valve. Ron has OS intakes with the seats bored. That cam combined with the head should do much better than 75HP. That exhaust sounds like it not performance oriented. That Hindle pipe is the first thing I'd try and see what the A/F is. At that point you can fool with fuel settings.

[CBJoe]

Ron, borrow Joe's new RS34's for a run  I like the Mikuni 29's - for a stock/near stock bike. You're choking it down maybe? Let it breathe more.

Not pulling my carbs off jerry unless you are going to come install them again

[MRieck]

Ron, borrow Joe's new RS34's for a run  I like the Mikuni 29's - for a stock/near stock bike. You're choking it down maybe? Let it breathe more.

Not pulling my carbs off jerry unless you are going to come install them again

I don't blame you. Are you using the reproduction 77/78 K insulators Joe?? Makes life easier and shortens the OAL of the intake tract.

[CBJoe]

Yep...77/78 Boots

Ron,  lets check your plugs Sunday after those pulls and see what they look like.  I'm trying to remember the Cam Timing numbers we settled with on your bike.  Did you save those notes?

[scottly]

I don't think the wonky A/F readings are caused by either the pipe, the cam timing, or the carb jetting, per se. I suspect the dyno run was done with the "bypass" cold start enrichment system, AKA choke on. With stock carbs, the choke is literally cutting off air going into the motor. With a bypass, air goes around the slide through a separate passage, where it sucks up fuel from a separate jet. A bypass enrichment system is most effective when the throttle is fully closed, and has the least effect when the throttle is WFO.
 

[Jerry Rxman Griffin aka MuthaF'er]

Never mind Ron. I am NOT removing my 34's or Joe's haha.

Mike, I agree. Exhaust first. One thing at a time. 

[MCRider]

Yep...77/78 Boots

Ron,  lets check your plugs Sunday after those pulls and see what they look like.  I'm trying to remember the Cam Timing numbers we settled with on your bike.  Did you save those notes?

Got it. We'll check the ignition timing with a strobe also. Its just static timed so far. Also review the advancer I'm using.

Last time it was on a good dyno, we got 79.8 HP and 55 Lbft TQ. using a MegaCycke pud cam (just above stocks) and the Marshall pipe.

[MCRider]

Oh yeah, from a good looks dept, the Marshall 2 tone megaphone flared out so far on the right it prompted Terry from Oz to suggest using if as the sidestand. UUgly.

[MCRider]

So plan is shaping up: examine oil pump filter, check and change plugs, tighten up the ignition timing, change oil. Take a guess at some re jetting.

Go to Ducati again. See if we can't get numbers like at V-Victory. 

While I save up to buy a Delvinick pipe.

[MRieck]

I don't think the wonky A/F readings are caused by either the pipe, the cam timing, or the carb jetting, per se. I suspect the dyno run was done with the "bypass" cold start enrichment system, AKA choke on. With stock carbs, the choke is literally cutting off air going into the motor. With a bypass, air goes around the slide through a separate passage, where it sucks up fuel from a separate jet. A bypass enrichment system is most effective when the throttle is fully closed, and has the least effect when the throttle is WFO.

I doubt that. When that plunger is raised it makes a loud, chugging sound. You would notice it unless you are deaf. Are you saying the plunger seals are leaking and not completely shutting off the enrichment circuit?

[scottly]

I don't think the wonky A/F readings are caused by either the pipe, the cam timing, or the carb jetting, per se. I suspect the dyno run was done with the "bypass" cold start enrichment system, AKA choke on. With stock carbs, the choke is literally cutting off air going into the motor. With a bypass, air goes around the slide through a separate passage, where it sucks up fuel from a separate jet. A bypass enrichment system is most effective when the throttle is fully closed, and has the least effect when the throttle is WFO.

I doubt that. When that plunger is raised it makes a loud, chugging sound. You would notice it unless you are deaf.

Or wearing ear muffs. Honestly, I don't recall any audible difference with the plunger raised on my FT with a VM36; I'll try to pay more attention next time I start it.
How are the plungers linked together when mounted on a rack? I've only experience with singles?
Let's see if the plugs are as black as the sniffer suggests. BTW, the probe on my sniffer is a length of 1/4" OD copper tube.

[PeWe]

I have used a CX-7 cam with 836, it woke up around 6500-7000 rpm. Very abrupt, I had to hold handle bar very hard when it kicked in.  This with 4-1 that became extra loud with CX-7.

+900cc, ported head with oversized valves and that cam should enter at least 85whp.

The compression my billet block + JE 71.25mm pistons deliver with RC295 profile is 190-195 PSI. Pistons from Dynoman for 24 5cc chambers.
I think they sell a kit as CR11:1 like my pistons might deliver with 22.5cc.

The engine has been in the 180 PSI area earlier with other cam and 836.

Hindle 4-2-1 work fine! Use the longer baffle, more sound not needed. It sings wonderful.

[scottly]

This was posted on another thread, but might apply here as well:

might apply to you... was chasing for a long time some intermittent bad running on my kz750 with VM26. At one point it started fouling fouling plug nr2, still couldnt find the fault, was driving me crazy. turns out the grub screw for the choke arm for that carb was a bit free so plunger was not returning fully when i closed the choke. sorted that, gave all choke plungers  a nice greasing, runs sweet now....

[CBJoe]

Hey Scott,   Plugs looked pretty good when we checked them. 



Ron...here’s a sweet picture...forgot I snapped a few in the nice light.   So purdy




Sent from my iPhone using Tapatalk

[scottly]

The #1 plug looks bone white, compared to the other three, but other than that there are no glaring issues. I think I would try going down one or two sizes on the mains without changing anything else carb-wise for the next dyno session. The dyno is for WFO main jet territory.

[MCRider]

Hey Scott,   Plugs looked pretty good when we checked them. 



Ron...here’s a sweet picture...forgot I snapped a few in the nice light.   So purdy




Sent from my iPhone using Tapatalk

Yeah, she does photograph well! 

[Jerry Rxman Griffin aka MuthaF'er]

How did the last carb sync turn out?

[CBJoe]

The #1 plug looks bone white, compared to the other three, but other than that there are no glaring issues. I think I would try going down one or two sizes on the mains without changing anything else carb-wise for the next dyno session. The dyno is for WFO main jet territory.

Hey Scott....I think that's an effect of the camera...they all looked pretty much the same when we pulled them. 

[Terry in Australia]

Oh yeah, from a good looks dept, the Marshall 2 tone megaphone flared out so far on the right it prompted Terry from Oz to suggest using if as the sidestand. UUgly.

Oh wow, I do remember that pipe Ron, it was about as ugly as a pipe could get. A Hindle would be my choice, closely followed by a Delkevic. I remember the owner of Dynobike here in Melbourne telling me he got an extra 20BHP from a Suzuki 1200 Bandit just by installing a Hindle and a K&N filter.

[MCRider]

How did the last carb sync turn out?

The VM29s do not have a way to sync the carbs while on the bike. You have to remove the carb tops and get into the guts. This is even disclosed in the VM29 manual. The way to do it is a "bench sync". Have the carbs on the bench, use a finishing nail or other shim to set one slide as the standard and then sync each one to that. When I bot my first set, the ones I am running now, I ran them as is and was very pleased. I have a new second pair with Rick Smith OldSkoolCarbs. He's cleaning them up and will perform the bench sync. But after my positive experience (10 years, 50,000+ miles) where I never had the desire to touch them, I don't think that's a problem.

Low speed responds to low speed jet changes, I think we'll be able to get it done that way.